The present disclosure is related to the field of tomography. More specifically, the present disclosure is related to the field of digital breast tomography (DBT), the interpolation of synthetic projection images from DBT data, and the use of such synthetic projection images.
For the diagnosis of breast cancer, radiology is generally used to obtain an image of the inside of the breast. A two-dimensional (2D) radiological image shows a projection of a tissue matrix, e.g. a breast for breast cancer diagnosis, onto a plane formed by a detector, from a radiation source. The radiological image is generally obtained by placing the object of interest between the X-ray emitting source and the X-ray detector, so that the rays reach the detector after passing through the object. The radiological image is then created from data provided by the detector, and represents the tissue matrix projected onto the detector in the direction of the X-rays.
In such a radiological image, an experienced practitioner can distinguish radiological signs indicating a potential problem, e.g. micro-calcifications, lesions, or other opacities in the case of mammography. However, a radiological image is derived from a two-dimensional projection of a three-dimensional tissue matrix. Tissue superposition may mask radiological signs such as lesions, and under no circumstance is the true position of the radiological signs inside the object of interest known; the practitioner having no information on the position of the radiological signs in the direction of projection.
Tomosynthesis has recently been developed to address these issues; it allows a three-dimensional (3D) representation of an object of interest to be obtained in the form of a series of successive slices. These slices are reconstructed from projections of the object of interest at different angles. For this purpose, the object of interest is generally placed between an X-ray emitting source and an X-ray detector. The source and/or the detector are movable, which means that the projection direction of the object of interest onto the detector can be varied. In this manner, several projections of the object of interest are obtained at different angles, from which a 3D representation of the object of interest can be reconstructed.
For each tomosynthesis projection image, the radiation doses of the X-rays are naturally less than those used for standard mammography. For example, by noting as D the radiation dose of standard mammography, and as N the number of projections used for tomosynthesis, the radiation dose used for each projection is of the order of D/N. While operating within this general constraint on tomosynthesis imaging, a tradeoff must be made between the number of tomosynthesis projection images and the radiation does used to acquire each individual projection image. Radiation dose is generally associated with higher X-ray image quality through improved contrast, up to saturation levels. However, greater numbers of projection images can improve tomographic 3D reconstructions, or rather, 3D reconstructions from limited number of projection images are subject to exhibit artifacts known as “streaking.” In reality, all iterative reconstruction techniques produce a “streak” artifact for each projection image used in the reconstruction. However, the intensity of the artifact diminishes with each additional projection image used in the reconstruction.
Additionally, techniques are known for creating synthetic 2D mammography images by reconstructing a 3D volume from the tomosynthesis projection images and then using that 3D reconstruction to enhance one of the acquired tomosynthesis projection images into the synthetic 2D mammography image. However, those techniques are limited to producing synthetic mammography images at the positions from which the original tomosynthesis projection images were acquired.